1. Field of the Invention
The present invention relates to a beamforming apparatus and a beamforming method to be used for performing beamforming of electromagnetic wave, light, sound, ultrasound in radars, sonars, ultrasonic diagnosis apparatuses and so on.
2. Description of a Related Art
Measurements regarding various states (physical properties, the distributions, etc.) of various objects and living things, distributions of objects, and environments are performed by using radars, sonars and ultrasonic diagnosis apparatuses. In order to realize proper measurements, beamforming is usually performed (in a reflection or transmission mode, etc.). Beamforming is also performed for measurements of various target motions (velocity, displacement, strain, acceleration, strain rate, etc.). In addition, beamforming is also performed on various energies used for treatments and repairing of various targets.
FIG. 4 shows the components in a typical beamforming apparatus. This beamforming apparatus includes a transmitting unit 101, a receiving unit 102, apodizing units 104 and 104′, and an addition unit 105 of signals. The units 101 and 102 are respectively equipped with delay units 103 and 103′. The delay units can also be equipped outside the units 101 and 102. The orders of the units in the beamforming apparatus can also be inverted. Further, more than two units can also be realized as one unit. The intensities, frequencies, bandwidths, and shapes of transmission signals are determined by the unit 101, and the reductions of noises and amplifications of reception signals are performed by the unit 102. The shape of the signals can also be changed by filtering, etc. Moreover, the intensities and shapes of the respective signals can also be changed by the apodization units 104 and 104′.
The number of the channels in the units determines available numbers of signals and array elements (2D or 1D) to be used independently. The actual number of additions of signals can also be determined in the unit 105. Various beamforming such as focusing (FIG. 5A) and steering (FIG. 5B) are performed by adding reception signals after controlling the delays of the transmission and reception signals in the units 103 and 103′.
As a related art, Japanese patent application publication JP-P2001-104307A (FIG. 1) discloses, for reception beamformers, the realization of the functions for controlling of the delays and amplitudes of signals in integrated circuit chips. All calculations as functions of time related to the delays and amplitudes (gains) are performed outside the chips. The data of delays and amplitudes are calculated in advance by a conventional computer and the data are simply used in the chips to set the functions of delays and amplifications. That is, the chips are equipped with the functions of the delays and amplifications.
However, in order to obtain the best measurement accuracy of target motion, spatial resolutions and contrasts of treatment and image, after designing the desirable point spread function (PSF), the beamforming that realizes the designed PSF should be performed at transmitting and/or receiving processes. In pasts, there exists no apparatus that realizes such beamforming. Usually, theoretical analyses or numerical calculations of electromagnetic fields and sound fields are performed to design the beamforming. However, after all, by changing the beamforming parameters such as the intensities, frequencies, bandwidths and shapes of the signals transmitted by the transmitting unit, the filtering of noises, amplifications (gains) and shapes of the signals received by the receiving unit, the number of the additions of the signals by the addition unit, apodization functions of the directions of propagation and array used by the apodization unit, delays of the directions of propagation and array used by the delay unit on the basis of the experiences, the beamforming apparatus is realized. Thus, the best beamforming cannot always be obtained. In addition, a spatially and temporally uniform or arbitrary PSF should be realized occasionally.